The present invention relates to a fuel injector and a method of producing same.
German Published Patent Application No. 197 36 682, for example, describes fuel injectors having a valve seat body which is inserted on the downstream end of the fuel injector into a nozzle body of the fuel injector from the downstream side. In the valve seat body they have a valve seat face which cooperates with a valve closing body to form a sealing seat. A weld is used for fixation. A swirl-producing module is situated upstream from the valve seat body and is positioned on the upstream side of the valve seat body with the help of a spring. The swirl-producing module is composed of a guide disk and a swirl disk which is situated between the guide disk and the valve seat body.
The weld between the valve seat body and the nozzle body must provide a seal while also resisting the force exerted by the fuel pressure and the spring force pressing the valve closing body onto the valve seat face. The valve seat body is pressed into the nozzle body and then welded. Because of the compression connection, which forms the basis for a welding operation of a reproducibly high quality, it is impossible to correct the position of the parts relative to one another. However, the quality of the sealing seat depends on the relative position of the central axes. Therefore, these parts are turned in a complex machining operation to ensure the required high precision.
To compensate for tolerances in position of the valve needle, the guide disk is mounted on the swirl disk so that it is displaceable radially. Therefore, a slight valve needle offset may be compensated.
German Published Patent Application No. 196 25 059 also describes a fuel injector with which the conditioning of fuel to be spray-discharged and the sealing seat are located together in a valve seat body. The valve seat body has a recess to guide the valve needle. Upstream from the valve seat face, fuel channels are introduced into the valve seat body through which fuel is spray-discharged in individual jets through a large opening. The valve seat body itself is machined in a turning operation and is pressed into the nozzle body from the downstream direction and then welded.
One disadvantage of the known fuel injectors is the lack of a possibility to compensate for tolerances in parts which occur due to positioning of the valve seat body. In particular, for the fuel injector known from German Published Patent Application No. 196 25 059, the position of the guide bore relative to the valve seat is extremely important. To achieve good guidance of the valve needle, the clearance is kept as small as possible. At the same time, however, compensation of tolerances is possible only through this clearance. Increasing the size of the clearance might ultimately allow vibration of the valve needle, which is undesirable. On the other hand, if the clearance is too small, the valve needle is subject to mechanical wear, grinding on the guide bore with each opening and closing operation of the fuel injector.
Both fuel injectors have the disadvantage that it is impossible to compensate for an angular misalignment in the valve needle. With the narrow play described here between the valve needle and the guide bore, this unavoidably results in tilting of the valve needle in the guide bore.
Another disadvantage is the requirement of the weld itself, which must have a high mechanical strength but at the same time also has a sealing function. This makes the process management, and in particular its monitoring, much more difficult.
The fuel injector according to the present invention has the advantage over the related art that the position of the valve seat is variable. In assembly of the fuel injector according to the method of the present invention, an accurate alignment is achieved. The valve seat body is held in this position and then welded there.
Another advantage is achieved due to the insertion of the valve seat body from the inside. The forces acting on the valve seat body are absorbed by the nozzle body. The weld is not under mechanical stress. The process management is thus greatly simplified, as is the inspection of the joint. A leakage test may be performed on the fuel injector by simply pressing on it.
Welding the swirl disk to the valve seat body reduces the positional tolerance in an advantageous manner. The position may be defined precisely by a centering mandrel. By joining the two parts, the swirl disk and the guide disk together with the valve seat body may be handled as one module. Likewise there is the possibility of preassembly, so that any valve seat module rejects is not picked as late as at the fuel injector production line.
In addition, use of a ball as a valve seat body is advantageous. The swirl-processing recesses are introduced into the ball. Use of a ball bearing balls, for example, reduces costs because they are inexpensive and are available in large numbers and in a uniform quality. Handling of the balls is simple because they need not be oriented a certain way when supplied for machining.